This invention relates generally to liquid drainage systems used on site for footings, open trenches or nitrification fields used as discharge points for septic tanks, and more particularly to a novel drainage system which is easy to install and which maximizes the size of a storage chamber or area for the liquid until it can be absorbed by or percolated into the surrounding soil.
In the past conventional drainage systems have typically comprised a horizontally extending perforated conduit placed within a drainage trench and surrounded by a quantity of loose aggregate material such as rock or crushed stone and covered with compacted soil. The space between the conduit and ground occupied by the aggregate serves to define a drainage cavity in fluid communication with the perforations of the conduit. An example of such a drainage system is found in the nitrification field of conventional ground absorption sewage disposal systems wherein effluent is discharged form a septic tank through the perforated vent pipe of a nitrification line which is surrounded by aggregate material such as rocks or crushed stone. The nitrification field creates a storage chamber or area for the sewage affluent until it can be absorbed by the soil.
These conventional systems suffer a number of drawbacks as discussed in U.S. Pat. No. 5,015,123 (owned by the assignee of this invention), and the novel drainage system described and claimed in the ""123 patent represents a substantial improvement over the conventional system. The description of that improved system as set forth in the ""123 patent is incorporated herein by reference in its entirety. Briefly, that system utilizes pre-assembled drainage line units illustrated in FIG. 2 of the patent in which loose aggregate in the form of lightweight materials is provided in surrounding relationship to a perforated conduit and bound thereby by a perforated sleeve member. These units used in combination with pre-assembled units illustrated in FIG. 3 of the patent which do not include the perforated pipe replace the gravel system used in the conventional systems as illustrated in FIGS. 4b and 4c of the patent to provide the storage chamber or area for the effluent until it can be absorbed by the soil. The system of the ""123 patent represents a substantial improvement over the prior conventional gravel system for the reasons set forth in the ""123 patent and has enjoyed substantial commercial success.
Recently, another drainage system has been proposed which includes a pair of drainage pipes such as those illustrated in FIG. 2 of the ""123 patent extending longitudinally within the trench and laterally spaced from each other to define an open storage chamber and a cover placed on top of and spanning the laterally spaced pipes to prevent top dirt fill from falling down into the storage chamber. While this system conceptionally shows some promise, the design of the cover has not been strong enough to support the weight of the top fill dirt and bends and deflects downwardly to decrease the size of the storage chamber and reduce the overall efficiency of the drainage system.
Thus, there is a need in this most recent proposal for a cover which has sufficient strength and stability to support the weight of the top fill dirt and thereby avoid the problem associated with prior covers. The cover of this invention as described and claimed herein below was developed to perform that task.
Accordingly, the primary object of this invention is to provide a drainage system which includes a pair of longitudinally extending drain pipes placed within a drainage trench laterally spaced from each other to define a liquid storage chamber therebetween and a novel cover placed on top of the drain pipes. The cover is sufficiently strong and stable to support the weight of the fill dirt placed on top thereof, thereby substantially maintaining the chamber at its original size for storage of the drainage liquid until it can be absorbed by the soil defining the bottom of the trench.
Another object of the invention is to provide the above drainage system wherein the novel cover includes two side portions extending longitudinally over and generally conforming to the shape of the drain pipes and a center portion connecting the two side portions to maintain the drain pipes in laterally spaced relationship, the cover further including reinforcing elements extending between the side portions and the center portion to prevent downward deflection of the center portion under the weight of the top soil. As a result the size of the chamber is maintained to create maximum storage area for the liquid drainage until it can be absorbed by or percolated into the soil at the bottom of the trench.
A further object of the invention is to provide various embodiments of the novel cover which can be used in the above described drainage system and wherein all of the embodiments contain reinforcement elements which prevent downward deflection of the cover under load.
Still another object of the invention is to provide a novel cover as described above wherein the cover includes a plurality of vented openings which allows the system to breathe to thereby retard development of the clogging mat within the chamber, that is the mechanical loss of infiltrative capacity at the soil surface interface due to suspended solids, bacteria growth and ferrous sulfide precipitation.
Other objects and advantages of the invention will become apparent from reading the following detailed description of the invention wherein reference is made to the accompanying drawings.